A different research direction focuses on layered models that iteratively predicts entity spans until none can be found. [1]} uses a fixed number of layers and updates spans representations using a novel neural architecture. [2]} designs a layered architecture that predicts entities at each layer and merges the word representations before applying the next layer. [3]} computes tag scores for each word and decodes the spans by applying the Viterbi algorithm multiple times on a previously extracted subsequence, starting from the full sentence.
